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This paper is devoted to the study of pollutant concentration distribution within urban-like geometries. By applying efficiency concepts originally developed for indoor environments, the term ventilation is used as a measure of city “breathability”. It can be applied to analyse pollutant removal within a city in operational contexts. This implies the evaluation of the bulk flow balance over the city and of the mean age of air. The influence of building packing density on flow and pollutant removal is, therefore, evaluated using those quantities. Idealized cities of regular cubical buildings were created with packing density ranging from 6.25% to 69% to represent configurations from urban sprawl to compact cities. The relative simplicity of these arrangements allowed us to apply the Computational Fluid Dynamics (CFD) flow and dispersion simulations using the standard k– turbulence model. Results show that city breathability within the urban canopy layer is strongly dependent from the building packing density. At the lower packing densities, the city responds to the wind as an agglomeration of obstacles, at larger densities (from about 44%) the city itself responds as a single obstacle. With the exception of the lowest packing density, airflow enters the array through lateral sides and leaves throughout the street top and flow out downstream. The air entering through lateral sides increases with increasing packing density.

At the street top of the windward side of compact building configurations, a large upward flow is observed. This vertical transport reduces over short distance to turn into a downward flow further downstream of the building array. These findings suggest a practical way of identifying city breathability. Even though the application of these results to real scenarios require further analyses the paper illustrates a practical framework to be adopted in the assessment of the optimum neighbourhood building layout to minimize pollution levels.

The present paper is aimed at the analysis of flow and pollutant dispersion in a portion of the Canal Grande (Grand Canal) in Venice (Italy) by means of both Computational Fluid Dynamics (CFD) FLUENT simulations and wind tunnel experiments performed at the University of Gävle (Sweden). For this application, Canal Grande can be viewed as a sort of street canyon where the bottom surface is water and bus boat emissions are the major source of pollution. Numerical investigations were made to assess the effect of the water surface on air flow and pollutant concentrations in the atmosphere. One of the challenges has been to deal with the interface between two immiscible fluids which requires ad-hoc treatment of the wall in terms of the numerical scheme adopted and the grid definition which needs to be much finer than in typical numerical airflow simulations in urban street canyons. Preliminary results have shown that the presence of water at the bottom of the street canyon modifies airflow and turbulence structure with direct consequences on concentration distribution within the domain.

4. Cooper, Ed

et al.

Etheridge, David

Mattsson, Magnus

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Wigö, Hans

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

The University of Gavle is currently involved in a project on saving energy in historic buildings (churches).An important factor in the determination of the natural ventilation rate is the adventitious leakage of the envelope. Measurement of leakage is therefore a key feature of the investigations. It was decided to adopt a new technique developed at the University of Nottingham (UNott). It is a pulse technique compared to the conventional steady technique.

The conventional technique consists of generating a steady and high pressure difference (50 Pa) across the envelope by means of a fan. Such pressures are rarely encountered in ventilation and this leads to errors in the low-pressure leakage. Furthermore the use of the conventional blower door technique in churches is difficult due to their large volume and the need to replace the doors.

The underlying principle of the UNott technique is described and examples of results are given. The most important advantage of the Unott technique is that the leakage is determined at the low pressure differences that are encountered with ventilation e.g. 4 Pa. This is made possible primarily by the fact that the effects of wind and buoyancy at the time of the test are eliminated by taking account of the pressure variation before and after the pulse.

For measurements in large buildings, a number of identical piston/cylinder units have to be operated simultaneously. The University of Gävle has developed a system whereby up to seven units can be used. Such a number is required for a leaky church and this is the first time this has been done.

6.

Fallenius, Bengt E.G.

et al.

KTH.

Sattari, Amir

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Fransson, Jens

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Studies are still required to understand how rural/marine wind remove ground-level pollutants released uniformly in street networks of high-rise urban areas. The link between building height variability and pollutant removal process still remains unclear. Several idealized urban-like neighbourhoods made of 9-row and 18-row small-scale high-rise square arrays (building width B = street width W, building packing density λp = 0.25) were first numerically studied with a parallel approaching wind and neglecting thermal effects. Normalized pollutant transport rates and pedestrian purging flow rate were applied to quantify the contribution of pollutant removal by mean flow and turbulent diffusion and their net purging capacity.

Results show that the prediction of isothermal turbulent flows agreed generally well with wind tunnel data. For 9-row arrays with building height variations (standard deviation of 0–57.1%) and the same average canopy height (H0 = 2.33W), pollutant removal mainly depends on mean flows. Larger standard deviations tend to induce better pedestrian ventilation. In comparison to small and large standard deviations, medium values of 14.3–42.9% may experience smaller purging capacity by horizontal mean flows but significantly enhance that by vertical mean flows. For arrays with uniform heights, lowering aspect ratios (H/W = 2.33 and 2.67–1.5) or increasing street lengths (9-row to 18-row) may enhance the contribution of removing pollutants by turbulent diffusions across canopy roofs which may be similarly important as that by mean flows. Although further investigations are still required, this paper clarifies the relationship between building layouts, height variability and removal potential of ground-level pollutants in high-rise urban-like geometries.

This paper analyses the contribution of mean flow and turbulence to city breathability within urban canopy layers under the hypothesis that winds from rural/marine areas are sources of clean air (inhale effect) and main contributors to local-scale pollutant dilution (exhale effect). Using Computational Fluid Dynamics (CFD) simulations, several idealized long streets flanked by tall buildings are investigated for wind flow parallel to the street axis. Aspect ratios (building height/street width) ranging from 2 to 4 and street lengths ranging from neighborhood scales (~. 1. km in full scale) to city scales (~. 10. km in full scale) are analyzed. To assess the inhale effect, the age of air concept is applied to quantify the time taken by a parcel of rural/marine air to reach a reference location within the urban canopy layer. To simulate the exhale effect, removal of pollutants released from a ground level source is considered. Numerical results agree with wind tunnel observations showing that a bulk portion of rural/marine air enters the streets through windward entries, a smaller part of it leaves through street roofs and the remaining fraction blows through the street aiding pollutant dilution. Substantial differences between neighborhood-scale and city-scale configurations are found. For neighborhood-scale models, pollutant removal by rural/marine air is mainly associated to mean flow along the streets. Breathability improves in streets flanked by taller buildings since in this case more rural/marine air is captured inside canyons leading to stronger wind along the street. For city-scale models, pollutant removal due to turbulent fluctuations across street roofs competes with that due to mean flows along the street. Breathability improves in streets flanked by lower buildings in which less rural/marine air is driven out and pollutant removal by turbulent fluctuations is more effective. Based on these findings, suggestions for ventilation strategies for urban areas with tall buildings are provided.

We regarded high-rise cities as obstacles and channels to wind. We first studied wind conditions and ventilations in idealized high-rise long street models experimentally and numerically with a constant street width (W = 30 mm), variable street heights (H = 2 W, 2.5W, 3W, 4W), variable street lengths (L = 47.4W, 79W. 333W, 667W) and a parallel approaching wind. The flow rates penetrating into windward entries are a little larger than the reference flow rate in the far upstream free flow through the same area with windward entries in all models. The stream-wise velocity decreases along the street as some air leaves upwardly across street roofs. Near the leeward entry, there is a downward flow which brings some air into the street and results in an accelerating process. In the neighborhood scale long streets (L = 47.4W and 79W), wind in taller streets is stronger and the ventilation is better than a lower one. For the city scale long streets (L = 333W and 667W), a constant flow region exists where the vertical velocity is zero and the stream-wise velocity remains constant. In such regions, turbulent fluctuations across the street roof are more important to air exchange than vertical mean flows. In a taller street, the process to establish the constant flow conditions is longer and the normalized balanced horizontal flow rate is smaller than those in a lower street. In the city scale long streets, the turbulence exchange rate can be 5-10 times greater than the mean flow rate. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.

It is an open question whether a street network of a city has a certain flow capacity characterizing the flow that can pass through the street network. It s our hypothesis that at least the simple street network has a certain flow capacity. With the purpose of exploring this we studied numerically and experimentally the flow capacity in some idealized long-street models continuously lined with buildings and exposed to a parallel approaching wind. The height of all the models is the same (H = 69 mm). Three groups of models were studied: models with the same uniform street width (W = H) but different lengths (L = 21.7H, 43.5H, 72.5H); models with the same length (L = 43.5H) but different uniform width (W = H, 2H, 4H); and models with a change of width at half distance, L/2. In the last of the three cases, the width of the upstream half was always the same (W1 = H), but there was a wider (W2 = 1.25H, 1.5H, 2H) or narrower (W2 = 0.75H, 0.5H) downstream half. We normalized flow rates by a reference flow rate equal to the flow rate through an opening far upstream with the same area as the windward entry. The normalized flow rate through the windward entry was about 1.0 in all cases. For a sufficiently long-street models, a flow balance is established, creating a fully developed region with a constant horizontal flow (flow capacity) and zero vertical mean velocity. The street length does not affect the flow capacity but as expected the width of the street affects the flow capacity.

Air infiltration in ancient churches and other historical and monumental buildings is of great importance considering moisture transfer, energy consumption, thermal comfort and indoor surface soiling. Two of the most established models for simulatingand predicting air infiltration in buildings are the Lawrence BerkeleyLaboratory (LBL) model and the Alberta air Infiltration Model (AIM-2). The applicability of these models in superimposing wind and buoyancy driven infiltration in large single zone buildings such as churches are evaluated in this study by comparing model predictions with field measurements in a 19thcentury stone church. Both tested air infiltration models yielded significant positive correlations between measured and predicted data, and it is concludedthat the AIM-2 model works better than the LBL model for the studied church. Both models tend however to over-predict the air infiltration rate significantly. The over‑predictions were larger in cases with high wind speed and it seems that the models are more fragile in wind dominating conditions. Inclusion of crawl space coefficients in the AIM-2 model improved however the predictions, especially at high wind speeds. It seems that models of the tested kind can be useful in predicting air infiltration in churches and similar buildings, but that some empirically attained model coefficients might need some adjustment to suit this kind of buildings better.

13.

Karimipanah, Taghi

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy engineering.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

This paper introduces a new wake analysis technique behind wind turbines, called pressure footprint (p-f) method, as a simple technique for wind tunnel experiments as well as for field measurements. It is based on the assumption that the pressure at ground is related to the total pressure at the hub height, which in turn can be correlated to the velocity deficit of the wake. The p-f method requires that the static pressure can be measured on the ground and for this purpose we here use a pressure plate with 400 pressure taps. A single wind turbine model was positioned in the middle of the plate and the pressures were measured using a scani-valve. The static and total pressures at hub height were also measured. The effect on the wake pressure footprint when varying the hub height was studied, and by an appropriate definition of the applied pressure coefficient the variation of the footprint size vanishes, which is an important first step in relating the footprint area to the velocity deficit in the wake. We also show the interaction of two wind turbine models, located on the same centre line, with varying reciprocal streamwise distance. With the current method the relative size between the upstream and the downstream pressure footprint remains constant with a factor of two. Next, we will investigate the correlation between the pressure footprint and the velocity deficit in the wake by performing particle image velocimetry measurements in the same setup.

15.

Kobayashi, Tomohiro

et al.

Ritsumeikan University.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Kotani, Hisashi

Osaka University.

Claesson, Leif

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Cross-ventilation is a complicated flow problem and difficult to control because wind exhibits a large degree of variation. The paper focuses on three items: a) to clarify and understand some of the basic characteristics of airflow as the influence of the opening size on the windward vortex and the leeward wake; b) to explore what information about the flow above the ground can be retrieved from pressure measurements on the ground; and c) to explore the accuracy of CFD. To meet these objectives, wind tunnel tests and CFD analyses were carried out. The studied object was a detached-house model provided with two openings. The size of these openings was changed in a wide range from narrow cracks to large openings. In the experiments, pressure measurements on the ground and PIV measurements were made. The internal flow was visualized with the sand erosion method. Pressure measurement on a floor surface is a relatively easy and an inexpensive method. In this experiment, the windward and leeward areas in particular were investigated to understand flow pattern and to confirm correspondence between flow pattern and recorded pressure on the ground. Those measurements show the difference in flow at different size openings in terms of the vortex on the windward side and the wake. When the size of the opening exceeded a certain value the near wake on the leeward side disappeared and on the windward side the vortex disappeared. The pressure distribution, flow pattern, and velocity profile are shown and compared between measurement and CFD.

The objective of the study was to create a simple CFD (Computational Fluid Dynamics) model of colliding isothermal jets from two identical ceiling diffusers facing each other and to study the influence of the distance between the diffusers on the resulting downward jet. The modelling was done using a commercial CFD (Computational Fluid Dynamics) code. Air flows were visualised with smoke in order to analyse the collision point and flow behaviour after the collision. Velocity measurements were carried out to obtain velocity profiles for the supply air diffusers to be used as initial conditions in the CFD simulations. In addition, measurements were made to determine velocity magnitudes in the collided jets at the occupied zone. Different turbulence models were used in the simulations and compared to the visualised and measured data. As a result a valid CFD model describing the behaviour of the two colliding isothermal jets was created. It was concluded that the CFD models adequately described the phenomena and provided useful data to be used in further studies.

17.

Li, Yuguo

et al.

University of Hong Kong.

Nielsen, Peter

University of Aaalborg.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Experts suggest that displacement ventilation can play a key role in providing better ventilation facilities in hospital environments. Designers need to consider that hospitals differ from conventional buildings in terms of ventilation needs. Exhaled infectious droplets or droplet nuclei of an infected patient need to be removed in general wards, waiting areas and isolation rooms to minimize transmission to health-care workers, other patients and visitors. The supply air is provided via a floor level opening at a low velocity in displacement ventilation The only way for air and pollutants to transport from the lower to upper zone is via the plumes that penetrate the interface. Displacement ventilation creates a flow pattern that makes it difficult for a pollutant released in the upper zone to spread to the lower one. The stable thermal stratification zone plays a dual role for displacement ventilation.

18.

Lim, Eunzu

et al.

Kyushu University japan.

Ito, Kazuhide

Kyushu University Japan.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

The concentration of contaminant in a room is not always uniformly distributed and hence it is important to evaluate the ventilation efficiency at various points or domains in the room to optimize and reduce the ventilation rate and the air-conditioning load of the room. Various ventilation indices have been developed to evaluate the ventilation efficiency of a point or a domain based on the contaminant concentration, for example, the age of air, the Scale for Ventilation Efficiency series, Visitation Frequency and Purging Flow Rate.

This paper presents a new concept of ventilation index, Net Escape Velocity (hereafter NEV), as an index for ventilation efficiency in an indoor environment. NEV represents the effective velocity at which the contaminant is transported/diluted from a target point. The objectives of the present work are to clarify the definition and concept of NEV on the basis of CFD simulation and to investigate the calculation methods of NEV. NEV is defined by contaminant concentration, convective flux and diffusion flux at a point. Using NEV normalized by the convection velocity at a target point, we can obtain information of the turbulent diffusion effect for removal/dilution contaminant and of the direction of diffusion flux which is the same or not with convective flux. It can be said that NEV is an index of ventilation efficiency that can evaluate the ventilation performance at a point and enable understanding of the forming structure of a contaminant concentration at a point.

In an experimental study, ventilation filters of high quality (F7 & F9) were tested regarding their efficiency in collecting birch pollen allergens in outdoor air. The birch pollen grain concentration in outdoor air was measured at the same time as pollen allergen and particle number concentrations were measured before and after the tested ventilation filters, thus enabling collection efficiency calculations. Simultaneously, the size distribution of birch pollen allergens was measured in outdoor air using a cascade impactor. The study confirms previous indications that pollen allergens may occur in outdoor air in particles much smaller than pollen grains, and can penetrate ventilation filters to a larger extent than might be expected. This entails that although the high quality filters collect most of outdoor air pollen allergens, a significant exposure dose to these allergens can occur in the indoor environment, especially when considering the fact most people stay much more indoors than outdoors. The study also confirms previous similar indications attained with grass pollen allergens, in that the allergenic particles tend to penetrate ventilation filters to a greater extent than other airborne particles.

22.

Mattsson, Magnus

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Broström, Tor

Högskolan på Gotland, Institutionen för kultur, energi och miljö.

Linden, Elisabet

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Lindström, Svante

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Air movements in churches affect the deposition rate of airborne particles on surfaces, and hence influence soiling of valuable artifacts of different kinds. Sooting from candles and the thermal comfort of people is also affected by indoor air velocities. In an experimental field study, two different heating systems were compared regarding their effect on room air velocities in a church: air-to-air heat pumps with indoor fan convectors vs. a combination of bench heaters and radiators. Hot-sphere and 3-D sonic anemometers were used to record air velocities in the church. Strong buoyant air flows were found both in the supply air flow path of the heat pumps and above the bench heaters, but the air velocities were rather low outside of these air currents. A ~25 cm thick downdraught air flow was found along walls and windows, with a magnitude that was similar at both heating systems and much larger than the outdoor air infiltration rate.

23.

Mattsson, Magnus

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Broström, Tor

Högskolan på Gotland, Institutionen för kultur, energi och miljö.

Linden, Elisabet

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Lindström, Svante

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

The air flow pattern and magnitude of air velocities in churches and other historic buildings are of interest since they influence the deposition rate of airborne particles on surfaces, and hence affect soiling of valuable artifacts of different kinds. Increased air movements might also cause enhanced sooting from candles and it has an influence on the thermal comfort of people. The type of installed indoor heating units is likely to be important here since these usually induce substantial air movements through natural or forced convection. In an experimental field study, two different heating systems were compared regarding their effect on room air velocities in a medieval stone church: air-to-air heat pumps with indoor fan convectors vs. a combination of bench heaters and radiators. Hot-sphere anemometers were used to record air velocities in the near-zone of the heat pumps and their surroundings, and 3-D sonic anemometers were used to measure downdraught air velocities at the surfaces of a wall and a window. Smoke was used to visualize air flow patterns.

It was found that the heat pumps caused strong buoyant air jets that rose to the ceiling, but that the air velocities were rather low outside of these jets. The bench heaters caused buoyant plumes, which also seemed to attain rather high air velocities and reach the ceiling. As regards downdraught along wall and window, no significant difference between the two heating systems could be seen, although there was a tendency towards slightly higher air velocities at these surfaces when the heat pumps were in use. Since the air flow pattern at the surfaces appeared similar, also the particle deposition mechanisms and soiling rate can be expected to be similar.

24.

Mattsson, Magnus

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Lindström, Svante

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Linden, Elisabet

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Frequently there is a wish to reduce the natural ventilation rate in churches in order to save energy and/or improve the thermal comfort. It is then often difficult to ascertain exactly which the dominating leaks in the building envelope are, and where tightening measures would be most effective. A number of different methods to identify these leakages are discussed here. It appears that valuable help can be attained by a combination of several measuring techniques, including IR-thermography, tracer gas and pressure measurements. These techniques can also be useful in verifying the effect of tightening measures.

25.

Mattsson, Magnus

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Lindström, Svante

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Linden, Elisabet

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Two different tracer gas techniques for quantifying the air change rate were tested in three naturally ventilated churches. The techniques were the decay method (or tracer gas dilution method) and a passive tracer gas method. It appeared that the room air in the studied churches tended to be fairly well mixed when the churches are heated, presumably due to strong natural convection air currents occurring at heat sources and cooler outer building surfaces. This seems to entail that both the decay and the passive method are fairly easy to apply during times of heating. It then doesn’t seem to matter much were the tracer gas is injected or where it is sampled. During non-heating periods, however, spatial differences in tracer gas concentrations were observed, making tracer gas measurements more difficult to perform.

26.

Mattsson, Magnus

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Claesson, Leif

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Lindström, Svante

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Hayati, Abolfazl

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

The air leakage of the building envelope of ancient churches and other historical and monumental buildings has impact on energy consumption, thermal comfort, humidity and indoor surface soiling. To measure the air leakage in such large and naturally ventilated single-zone buildings is however challenging, especially due to wind and buoyancy (stack) induced disturbances. This study describes experiences in this regard, attainedat field tests where the fan pressurization technique (“Blower door”) was employed. Reference is made to the European test standard EN 13829. Also results of wind-tunnel tests are utilized. It is shown that both buoyancy and wind at commonly occurring conditions can cause significant uncertainty in fan pressurization tests, and that some of the directions in the standard might need to be strengthened or amended. While the uncertainty in measured air leakage rate at the standard (high) pressure of 50 Pa may be small, the predictions of the air leakage rate occurring at realistically (low) indoor-outdoor pressures tend to suffer from significant uncertainty. That uncertainty is then conveyed to later utilizations of the test results, e.g. building energy modeling and prediction. It is also shown that the wind induced pressure at buildings like churches extends a considerable way out into the surroundings of the building; in the order of two times the building height. This has particular importance when choosing a reference point for outdoorpressure measurement.

27.

Nyman, Hans

et al.

Mälardalen University.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

A model tunnel (approximately ten hydraulic diameters) with different designs of the tunnel mouth has been placed in a wind tunnel and has been subjected to the effects of external wind by varying the wind direction at the mouth of the tunnel. In the experimental oriented study pressures have been measured and the airflow has been made visible with smoke and by the sand erosion method (semolina). The relation between the flow ratio and the direction of the wind has been explored. When the wind is blowing parallel to the tunnel, the tunnel flow is about 70% of the reference flow (the undisturbed flow due to the wind through an area corresponding to the tunnel cross section). This result holds for the length of this tunnel. For longer tunnels it will decrease due to increased friction. When the angle at which the wind is blowing increases, the tunnel flow decreases. The pressure measurements made it possible to quantify some of the phenomena which were observed in the visual trials. A large under-pressure was measured just outside the mouth of the model tunnel on the side of the tunnel corresponding to the separation in the visual trials. In front of the tunnel, a pressure increase due to the braking of the airflow was measured. The position of the pressure increase moved depending on the internal resistance in the tunnel. If the resistance in the model tunnel was high, the over-pressure in front of the mouth of the tunnel was higher and further from the opening. When the internal resistance was reduced (corresponding to e.g. a very short tunnel) the over-pressure decreased and moved closer to the tunnel opening.

Elderly churches have a unique shape with their high towers and long naves. There seems to be few if any reported measurement of pressure distribution on churches. Churches are naturally ventilated buildings and therefore when the wind speed is high the wind becomes an important driving force for ventilation. A model in scale 1: 200 was built of a 19th century Swedish church provided with a crawl space.The pressure on the façade of the model was recorded in 42 points. With the aim of studying the ventilation of the church, dedicated measuring points were located on windows, doors and in the positions corresponding to the location of the openings in the crawl space. Some field trials were undertaken with the scope of measuring the time history of the static pressure on the façade in some positions corresponding to measuring points on the wind tunnel model. Examples of these measurements are reported in the paper. With the aim of measuring the “region of influence” on the ground caused by the church, also the static pressure on the ground was recorded in the wind tunnel tests. The static pressure on ground was recorded with a pressure plate provided with 400 pressure taps arranged in a quadratic pattern.

32.

Sandberg, Mats

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Mattsson, Magnus

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Etheridge, David W

University of Nottingham, UK.

Claesson, Leif

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Elderly churches have a unique shape with their high towers and long naves. There seems to be few if any reported measurement of pressure distribution on churches. Churches are naturally ventilated buildings and therefore when the wind speed is high the wind becomes an important driving force for ventilation.

A model in scale 1:200 was built of a 19th century Swedish church provided with a crawl space. The pressure on the façade of the model was recorded in 42 points. With the aim of studying the ventilation of the church dedicated measuring points were located on windows, doors and in the positions corresponding to the location of the openings in the crawl space.

Some field trials were undertaken with the scope of measuring the time history of the static pressure on the façade in some positions corresponding to measuring points on the wind tunnel model. Examples of these measurements are reported in the paper.

With the aim of measuring the “region of influence” on the ground caused by the church, also the static pressure on the ground was recorded in the wind tunnel tests. The static pressure on ground was recorded with a pressure plate provided with 400 pressure taps arranged in a quadratic pattern.

33.

Sandberg, Mats

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Neophytou, Marina

University of Cyprus.

Fokaides, Paris

University of Cyprus.

Panagiotou, I.

Ioannou, I.

University of Cyprus.

Petrou, M.

Wigö, Hans

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Linden, Elisabet

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Soiling of surfaces in historical buildings by deposition of particles is a common problem. Minimizing soiling is an important goal for conservation of structures and objects. The surfaces give rise to an interference with the air motions along the surfaces. Properties of surfaces may therefore influence the particle deposition. It is well known that with increasing roughness of the surfaces the particle deposition rate increases. The properties of surfaces in historical buildings are not well documented. We have investigated samples of surfaces finished by wood float finish, steel float finish and brushed finish. As a reference we have used an MDF board. The geometrical properties of the surfaces have been documented by using the stripe projection method. The resistance to airflow along the surface and the turbulence generated by the surfaces has been investigated by recording the boundary layer flow over the surfaces in a special flow rig. The work reported is part of a project where the process of soiling is studied both in laboratory and in field studies. The air velocity adjacent to the surfaces will be recorded with both PIV (Particle Image Velocimetry) and hot-wire technique. The temperature gradient close to the walls will be recorded with cold-wire technique.

35.

Sandberg, Mats

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Wigö, Hans

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Claesson, Leif

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, BMG Laboratory.

Cehlin, Mathias

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Energy engineering.

Climate Change is a global phenomenon that has a global scale impact. The current trend of climate change towards the warming of the globe has resulted in various changes in the geological, climatology, social, economical, and biological processes worldwide. Temperature of the globe has increased due to various factors, but anthropogenic plays a major contribution through the heavy input of Greenhouse gases. One of the world’s most remote regions that have been affected by most of the anthropogenic stresses on environmental services is the Arctic Region. The Arctic Region has shown various drastic changes and has shown to be effected by various anthropogenic activities that take place elsewhere. These changes include the ozone hole (resulting from ozone degrading compound emitted heavily by anthropogenic demands ), the accumulation of various persistent and volatile pollutants (i.e. POPs) , and the meltdown of the polar ice (among others) . These drastic changes are well perceived and well projected for future preparations. However, the question still remains if these impacts would only accelerate change. This paper aims to discuss if these changes are accelerating or happening at a constant rate. In addition, this paper aims to only focus on changes due to global warming and climate changes phenomenon.

With the fast-growing use of nanoparticles (NPs) in a wide range of production andmanufacturing processes, and great health and environmental risks associated to NPs, it is important totreat the industry-produced NPs in a proper way. Ventilation of industrial workplaces lies within theconcept of sustainability challenges for the development of nanoproducts. Due to the decreased grainsize of material to nano limits and thus the appearance of either new or changed properties, health riskof workers in such environments is critical concerning the complicated and unknown characteristicsof nanoparticles. There is great evidence over the past few years that ultrafine particles and especiallyNPs in the breathing air are strong toxins. Different mitigation measures for air-borne nanoparticles inindustrial workplaces are substitution, engineering controls such as ventilation and provision of personalprotective equipment. In this paper selection criteria for ventilation systems and different ventilationmethods (hood ventilation and global enclosure/room ventilation systems) as engineering controlsof nanoparticles within industrial enclosures will be reviewed. Novel methods for improvement ofventilation efficiency in general and industrial work places with an eye on ventilation of nanoparticleswill be presented.

38.

Sattari, Amir

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Fallenius, Bengt E. G.

KTH.

Fransson, Jens H. M.

KTH.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Optimal control of inlet jet flows is of wide applicative interest in order to enhance mixing and reduce stagnation in a ventilated room. The general approach in mechanical ventilation is to use a constant flow rate forced convection system providing the ventilation air. This type of ventilation may cause several problems such as draught, stagnation at certain occupied locations, and subsequently low ventilation efficiencies. An alternative to increase the ventilation quality that has been of interest in this study is to introduce flow variations, which is considered as a potential to reduce stagnation and increase efficiency of the ventilation. The study was conducted as a model experiment in a small-scale, two-dimensional (2-D) room model with dimensions 30´20´0.9 cm3 with water as operating fluid. The size of the model made it possible to investigate the 2-D velocity vector field within the entire room using Particle Image Velocimetry (PIV) method and further consequent dynamical and statistical analyses have been done from the resulted PIV vector fields. The comparison between cases of constant flow rate and flow variations have been conducted for the cases of two set of base flow rates and for each one, the cases of constant flow rate and flow variations with frequencies of 0.3, 0.4 and 0.5 Hz, is considered. In this investigation we show that the calm region, with a large stagnation zone, without pulsating inflow condition becomes more active in the sense that the stagnation points are moved and that the small-scale structures are grown for increasing pulsation frequency.

39.

Sattari, Amir

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

The use of supply jet flows is the most common type of air distribution for general ventilation. Usually the supply flow rate is constant or slowly varying (VAV-systems) to cope with a varying load. A novel air distribution method, with the potential to reduce stagnation and to increase the ventilation efficiency, is to introduce rapid flow variations (pulsations). This paper reports on a fundamental study of this type of air distribution. The purpose of the study was to explore the effect of flow variations on stagnant zones and the levels of the turbulent kinetic energy and the relative turbulence intensity. A small scale room model is used that consists of an enclosure with a ventilation supply at the bottom and an extract at the top of the opposite wall. Water was used as an operating fluid and the model had a design which mainly generated a two-dimensional flow. The size of the model made it possible to investigate the two-dimensional velocity vector field using the Particle Image Velocimetry (PIV) method in regions corresponding to occupied regions. Further post processing was conducted from the resulting vector fields. The comparison between cases of constant inflow and pulsated inflow (flow variations with frequency of 0.5 Hz) was conducted for three domains: two belonging to the far-field occupied zone and one belonging to the near-field, downstream of the supply wall jet.

40.

Sattari, Amir

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Sandberg, Mats

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

The use of supply jet flows is the most common type of air distribution for general ventilation inindustrial premises. Usually the supply flow rate is constant or slow varying (VAV-systems) to copewith a varying load. A novel air distribution method, with the potential to reduce stagnation and toincrease the ventilation efficiency, is to introduce rapid flow variations (pulsations). In the paper wereport on a fundamental study of this type of air distribution. The purpose of the study was to explorethe effect on stagnant zones and the levels of the kinetic energy and the relative turbulence intensity.The study was conducted in a small-scale, two-dimensional (2-D) room model with water as operatingfluid. The size of the model made it possible to investigate the 2-D velocity vector field in certainoccupied regions using Particle Image Velocimetry (PIV) method and further consequent analyseshave been done from the resulted vector fields. The comparison between cases of constant inflow andpulsated inflow (flow variations with frequency of 0.5 Hz) have been conducted for three domains,two belonging to the far-field occupied zone and one belonging to the near-field, downstream of thesupply wall jet.

41.

Smedje, Greta

et al.

Uppsala University.

Mattsson, Magnus

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Several studies have found that indoor air quality (IAQ) in schools is often poor and may affect the health of the pupils. Building ventilation is a means to reduce pollutant indoors but different designs should be evaluated for their effectiveness in different environments. In a field experiment performed in four classrooms in one school building we alternately supplied the air according to the mixing and displacement mode and collected information on exposures, pupils’ perception of IAQ and climate, health symptoms and performed clinical examinations. At breathing height, room temperature, relative humidity and the concentration of CO2 and cat allergen were similar in the periods with each ventilation type. The children perceived indoor air quality as similar in the two ventilation regimes, and there were few differences in symptom reports or clinical parameters. However, the pupils reported more eye symptoms during displacement ventilation.

The design of retrofitting strategies for historical buildings involves various challenges. The aim is often not only to save energy while providing acceptable indoor conditions for its users, but also to preserve the building and potential cultural artifacts, making it a multi-criteria issue, with multiple demands on the simulation tools and methods. This paper describes one way to fulfill on these demands through a serial, stepwise simulation process and a special tool, designed for that process. A case study, performed with the use of the method and tool, is presented. The results show that the method is workable and provides good agreement between simulated results and measured data.

43.

Widström, Torun

et al.

The Royal Institute of Technology, Stockholm, Sweden.

Mattsson, Magnus

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

In historical buildings, to an even greater extent than in modern buildings, the energy performance is connected to other aspects, such as moisture performance and damage risks. Here building simulation is of value, but it also faces some challenges in the form of complexity, flexibility and stability that need to be overcome in order to render useful results. This paper suggests a new, serial approach to the simulation process and presents a new simulation tool that makes it possible.

44.

Widström, Torun

et al.

The Royal Institute of Technology, Stockholm, Sweden.

Mattsson, Magnus

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

When simulating historical buildings, available tools tend to be intended for simulations of either of two kinds: whole building simulations of energy-/moisture performance, from which we can determine general conditions that may give an indication of potential damage risks, though unspecific, or detailed simulations that look into what takes place at specific points/materials, which provides us with knowledge about the specifics but without much context. Both are efficient scientific methods, but when dealing with reality we need both perspectives simultaneously. This paper describes multi-criteria simulations that take this into account, using a new tool integrating display of specific moisture-connected risk-factors into whole building simulations, providing a coherent basis for decision-making when retro-fitting, and compares the results to case-study measurements.

45.

Wigö, Hans

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.

Air movement in an indoor space may be experienced in very different ways. For persons feeling cool, air movement tends to be perceived as draught, whilst when feeling warm air movement may provide a desired cooling effect. In the transition zone it therefore seems difficult to use constant air velocity as a tool for cooling without creating draught problems. One possible way to use air movement as a method to improve thermal comfort, without resultant draught problems, could be to use intermittent air velocity instead of constant velocity. This new cooling method was implemented in a high school in Sweden and evaluated during spring (April) and autumn (September). The present paper reports results from two field experiments where subjects were exposed to velocity variations. The analysis shows significant effects of velocity condition on thermal comfort and air quality. In summary, people exposed to velocity variation perceived the air as cooler and fresher compared with those exposed to constant low velocity and very few classified the air movement as draught. A further conclusion is that even the pupils who were exposed to velocity variation wanted slightly more air movement.

46.

Wigö, Hans

et al.

University of Gävle, Faculty of Engineering and Sustainable Development, Department of Building, Energy and Environmental Engineering, Building science - installation technology.